Life in extreme environments is possible through multilevel adaptations to physical and biotic stresses. At high elevations, species face numerous challenges, besides low oxygen levels, but previous studies have focused on genetic and physiological adaptations to chronic hypoxia while overlooking other key strategies for thriving in alpine landscapes. Here, we investigate resource-use trait adaptations to extreme elevations using pikas as a model, lagomorphs distributed up to 6200 metres and reaching maximum diversity on the Qinghai-Tibet plateau, the highest plateau on Earth. Specifically, we assess cranial evolution in pikas using geometric morphometric and phylogenetic comparative techniques to determine whether adaptations among high-elevation biota shown at the molecular and physiological levels also occur in resource-use traits. We further explore the roles of two contrasting lifestyles (burrowing and rocky-dwelling) in cranial evolution. We found that alpine species exhibit striking phenotypic specialization to distinct microhabitats. Contrary to physiological and genetic adaptive convergence, we show that the cranium has undergone adaptive divergence likely reflecting past resource competition in highlands and long-term association with alpine landscapes. Our analyses also reveal that the evolution of burrowing lifestyle allows high-elevation pikas to explore novel niches and boosts their phenotypic diversification. In addition to cold and hypoxia tolerance, high cranial specialization, the appearance of burrowing habits, and strong niche separation explain how pikas overcome alpine stresses and flourish on the highest plateau on Earth. By contrast, when moving to spatially complex and heterogeneous vegetation zonation, pikas exhibit generalist skull forms able to exploit diverse habitats. These findings mirror previously reported intraspecific patterns in mammals, suggesting a general morphological response in resource-exploiting traits to cope with distinct selection pressures across elevation zones. Phenotypic diversity is further constrained by rocky habitats, resulting in convergent skulls. Our study highlights that adaptations to extreme environments occur at multiple levels of organization, but can lead to distinct evolutionary paths depending on which selective forces they respond to. The evolution of burrowing behaviour represents a landmark in the evolutionary history of pikas. We further show that rocky habitats impose strong ecological pressures, leading to convergent responses in resource-use traits, which is rarely documented in mammals.

Ochotona_landmarks_157ind.TPS This file contains the landmarks of 157 individuals of Ochotona used to perform the geometric morphometric analyses. Ochotona_traits.csv This file contains species, subgenus, elevation zone and lifestyle information for the 157 individuals of Ochotona Ochotona_phylogeny_31species.tre Tree with 31 pika species based on four genes (cytb, COI and ND4, ILRPB1).